Background: Optimizing the needle position using ultrasound (US) instead of electrical nerve stimulation (NSt) is increasingly common for perivascular brachial plexus block. These two methods were compared in a prospective, randomized, single-blinded controlled trial regarding effectiveness and time of onset of peripheral nerve blockade.
Methods: After puncture (penetration of neurovascular sheath and complete insertion of needle) 56 patients were randomly assigned to either the US group (finding the needle tip in transpectoral section, short axis, correction of needle position if local anesthetic spread was insufficient) or the NSt group (target impulse reaction in median, ulnar or radial nerve of 0.3 mA/0.1 ms, if necessary correction of position before injection of local anesthetic) to verify the needle position. All patients received 500 mg 1% mepivacaine. Sensory and motor blocks were tested by single nerve measurements (SNM) 5, 10 and 20 min after finishing the injection, where 0 represents minimal and 2 maximal success of the block.
Results: Single nerve measurements were analyzed using repeated measures ANOVA. The mean results of cumulative SNMs were significantly higher in the US group at all measurement times. Sensitivity US/NSt: 5 min: 3.36±2.32/2.63±1.87; 10 min: 5.45±2.41/4.21±2.45; 20 min: 7.30±2.02/6.43±2.43, p=0.015, motor function US/NSt: 5 min: 3.91±1.81/3.02±1.67; 10 min: 5.27±1.66/4.05±1.70; 20 min: 6.64±1.37/5.50±1.90, p<0.001. At the beginning of surgery complete nerve blockade was achieved in 89% in the US group and 68% in the NSt group (p=0.006), 3 (US) versus 7 (NSt) patients needed supplementation and 3 (US) versus 11 (NSt) patients needed general anesthesia (p=0.022). To achieve the nerve block took approximately 1 min more in the US group (p=0.003).
Conclusion: The use of ultrasound in perivascular brachial plexus blocks leads to significantly higher success rates and shorter times of onset.